Muslims pray during a prayer service held at the Islamic Center of America in Dearborn, Mich., in April. The American Civil Liberties Union has accused the FBI of racial, ethnic, and religious profiling, including the Muslim population in Michigan.

In a letter to US Attorney General Eric Holder Thursday, the ACLU pointed to “growing evidence … that the FBI is illegally and unconstitutionally targeting innocent Americans for investigation based upon their race, ethnicity, national origin, religion, and political activities protected under the First Amendment.”

Over the years since the terrorist attacks of 9/11, tensions between civil liberties organizations and domestic security agencies charged with preventing additional attacks have steadily increased. The same period has included a series of incidents in which alleged Muslim-American terrorists – particularly so-called “lone wolves” – have been thwarted in their attempts through the use of paid informants posing as fellow jihadis.

Meanwhile, the ACLU has filed numerous Freedom of Information Act (FOIA) requests – some backed up with lawsuits – to find out how the FBI is using racial and ethnic data as part of its investigations.

“The documents we have started to receive confirm our worst fears,” ACLU officials wrote to Attorney General Holder. “Although often heavily redacted, these documents, obtained from a number of different field offices, demonstrate that FBI analysts are using improper and crude racial stereotypes regarding the types of crimes committed by different racial and ethnic groups and then collecting demographic data to map where people of those racial or ethnic groups live.”

The result, charges the ACLU, has been “racial profiling on an industrial scale.”

For example, information obtained through one FOIA action shows that an FBI field office in Detroit sought authority in July 2009 to collect information and evaluate domestic terrorism threats “because Michigan has a large Middle-Eastern and Muslim population, [and] it is prime territory for attempted radicalization and recruitment” by State Department-designated terrorist groups originating in the Middle East and Southeast Asia.

In response to the ACLU report, the FBI stated flatly that it “does not investigate individuals, groups, or communities based on ethnicity or race.”

But in a statement, the FBI also noted the reality of the post-9/11 world as it sees it.

“Certain terrorist and criminal groups target particular ethnic and geographic communities for victimization and/or recruitment purposes,” the FBI said. “This reality must be taken into account when determining if there are threats to the United States.”

“To fulfill its national security mission, the FBI cannot simply wait for people to report potential threats,” the FBI statement continued. “To be threat-based and intelligence driven is to find previously undetected criminal and terrorist threats ... Just as putting push pins on a map will allow a local police chief to see clearly where the highest crime areas are, combining data that is lawfully collected into one place allows connections to be identified that might otherwise go unnoticed.”

Arab and Muslim American officials are not satisfied with such answers.

"To map Arabs and Muslims as suspect communities tells us that the FBI believes that we are predisposed to criminality, which is not only untrue but is also an inaccurate means of investigating crime,” the Michigan office of the Council on Islamic Relations said in a statement Friday.

"I understand that it's the FBI's job to protect the safety of our nation, and we are part of that,” Mr. Hamad said. “Safety is everyone's responsibility. But if we're going to truly be partners in this, then you can't treat us as suspects. You can't have it both ways – we can't be a partner and a suspect at the same time."

In addition to Arab-American and Muslim communities in Michigan, the ACLU also pointed to what it sees as racial profiling as part of FBI investigations of “Black Separatist” groups and recent African American population increases in Georgia, Russian and Chinese organized crime operations in San Francisco, and Hispanic communities in several states faced with threats posed by the Mara Salvatrucha, or MS-13, street gang.